I. Field of the Invention: This invention relates generally to an outboard motor drive system for a marine craft and more particularly to an improved outboard motor design incorporating a surface drive to enhance the performance characteristics thereof.
II. Discussion of the Prior Art: A typical, prior art, outboard motor assembly for a marine craft comprises a power head including an internal combustion engine, a vertical drive shaft and a lower unit, including a transmission and propeller shaft assembly and which is attached by suitable brackets to the transom of the craft. The downwardly extending engine drive shaft, the transmission and the propeller shaft are contained within a housing, the lower end of which extends below the keel of the boat such that, when operating, the propeller is totally submerged. Steering is accomplished by pivoting the motor assembly about a vertical axis running through the transom mounting bracket.
Another form of drive for a marine craft is a so-called stern drive or inboard/outboard drive. In this drive arrangement, the engine is located totally within the hull of the craft and the engine's shaft extends through the transom and is coupled to a transmission and comprising two bevel gears and an intermediate vertical shaft housed in a gear case and used to transmit the engine's output to a propeller again located below the keel of the watercraft. Steering is accomplished by rotating the external unit (outdrive) relative to a vertical axis passing through a mounting bracket attaching it to the transom of the vessel. Typical outdrive arrangements ar shown in the Bergstedt Patent No. 2,977,923, the Hurst Patent No. 3,893,407 and the Lohse Patent No. 3,888,203. In these prior art arrangements, the lower unit extends below the bottom of the boat's keel and thus create a drag which detracts from the forward speed and overall performance of the boat.
More recently, several articles have been published in various boating magazines describing the surface drive invention of Howard Arneson. In such a surface drive, the engine's output shaft is made to pass through the lower portion of the boat's transom in a generally horizontal disposition and is coupled through a universal joint to a propeller shaft which is journaled for rotation within a propeller shaft extension housing. A ball joint surrounds the universal joint which permits limited vertical and horizontal pivoting of the prop shaft extension housing to permit it to be tilted in a vertical plane or to be used for steering by shifting its position in a horizontal plane. The surface drive is configured so that approximately one-half of the propeller is above the surface of the water and the entire outdrive is disposed above the bottom of the boat's keel. As such, the outdrive does not create an appendage drag to adversely impact the craft's performance.
The specifics of the Arneson surface drive may be discerned from reading the Arneson U.S. Pat. No. 4,544,362. The Adams et al Patent No. 3,933,116 cited in the aforereferenced Arneson patent is also of interest as it relates to a surface drive assembly for use with an inboard engine on a marine craft.